Valves of the type to which the invention is directed are sometimes termed "meter and curb valves" or "plug valves" and have been commercially available for many years. They have been widely utilized in pipeline flow containing natural gas or other fluid substances. A common construction, employs a tapered plug valve arcuately operable in a conical body well. A biasing member such as a spring or the like forces the plug axially downward within the well. The body includes inlet and outlet passages separated by the well. For purposes of regulating flow, the plug includes a lateral thru-port alignable with the body passages. Valve operation comprises arcuately displacing the plug to either align or offset the thru-port of the plug with respect to the axis of the body flow passages. Exemplifying such valves are the disclosures of U.S. Pat. Nos. 3,360,236 and 3,806,087.
While such valves have functioned well, they are generally characterized as not being cost effective from the standpoint of manufacturing costs, are not inherently fire resistant, have less than optimum flow characteristics, tend to have higher than anticipated operating costs and require a modest amount of lubrication over the operating life of the valve.